Protein organization of rat synaptic plasma membranes and synaptic vesicles: a one- and two-dimensional study

Effects of diisopropyl phosphofluoridate, sarin and soman on the accessibility of proteins, in the electroplax membrane, to lactoperoxidase-catalyzed iodination

Anticholinesterases (anti-ChE) have some effects on biological properties including behavior, vision, and electroencephalograms, which are often long lasting and which do not appear to be due to cholinesterase (ChE; EC 3.1.1.7) inhibition, but which may be due to alterations in the organization and/or functioning of the cellular membrane. We assessed the effects of anti-ChE agents on the asymmetric organization of proteins in the innervated (excitable) and in the non-innervated (non-excitable) plasma membrane of the electroplax from the electric eel. Lactoperoxidase-catalyzed iodination (LCI) was carried out under impenetrable conditions in intact electroplax (where protein exposure on the external surface is monitored) and in split electroplax (where total protein labeling on both the external and internal monolayers of the plasma membrane bilayer is monitored). Labeling in split electroplax was much greater than in intact electroplax for all molecular weight groupings of proteins (30,000 to greater than 200,000). The anti-ChE agents diisopropyl phosphofluoridate (DFP; 10(-3) M), sarin (10(-4) M) and soman (10(-4) M, 10(-6) M, 2.5 x 10(-9) M) did not alter permeability, protein content or the electrophoretic pattern of the plasma membrane proteins of the electroplax. DFP, sarin and 10(-6) M soman (but not 2.5 x 10(-9) M or 10(-4) M soman) increased labeling of some of the molecular weight fractions in the non-innervated plasma membrane as monitored by LCI in intact electroplax. Under these same conditions, DFP and 10(-4) M soman increased labeling in the innervated plasma membrane while 10(-6) M soman decreased labeling. When LCI was carried out in split electroplax, 10(-4) M soman caused a decrease in labeling in both the innervated and non-innervated plasma membrane indicating a decrease of exposed proteins on the cytoplasmic surface of the plasma membrane. These concentrations of the anti-ChE agents caused almost complete ChE inhibition in the electroplax cells, except for 2.5 x 10(-9) M soman which caused little or no inhibition. These results suggest that alterations in protein asymmetry, as monitored by LCI of accessible proteins, are not directly due to ChE inhibition. These changes in organization of membrane proteins could contribute to a variety of effects of anti-ChE agents which are not due to ChE inhibition.

A hemagglutinin specific for sialic acids in a rat brain synaptic vesicle-enriched fraction

A hemagglutinating activity was detected in a synaptic vesicle-enriched fraction prepared from adult rat brain, using trypsinized glutaraldehyde-fixed rabbit erythrocytes. The specific activity of the fraction, in two series of experiments, was 7.5 and 16-fold higher than in the other subcellular fractions. The activity was absent from the synaptosome cytosol. In a study using twenty-five different carbohydrates and glycoproteins, best inhibitors were N-acetylneuraminic acid and N-glycolylneuraminic acid, together with bovine submaxillary mucin and a glycopeptide fraction prepared from rabbit erythrocyte membranes. The activity was thermolabile and very sensitive to proteolytic enzymes (but insensitive to neuraminidase) indicating that a protein (agglutinin) is responsible for the activity. Experiments using detergents and high ionic strength showed that the agglutinin is tightly bound to membranes, inactivated by the so-called non denaturing detergents, and stable in diluted sodium dodecyl sulphate. Hypotheses are discussed on the possible function of the agglutinin.